1. Field of the Invention
The invention relates to a road milling machine, in particular small milling machine, for working road surfaces.
2. Description of the Prior Art
Such small milling machine is known, for example, under the designation Wirtgen W 50 DC. The basic design of a generic road milling machine is known from DE 196 31 042 A1.
The small milling machine comprises a cantilevered milling drum which is mounted at the machine frame in a drum casing and can be driven by a milling drum drive.
The known milling drum drive comprises a drum gearbox that is arranged in part inside the drum casing and in part outside of the drum casing. To this effect, the drum gearbox is attached at a front wall of the drum casing by means of a connecting flange.
In a known drum gearbox according to DE 10 2010 014 529 A, at least one part of the reduction gearbox is arranged in the gearbox housing located in the drum casing so that, in the upper area of the gearbox housing, which is eccentric relative to the output shaft of the drum gearbox, the cantilevered milling drum encloses said gearbox housing with a relatively small gap. Such gearbox housing protruding into the drum casing has the disadvantage that milled material penetrating into the interior of the milling drum collects in the narrow gap between the gearbox housing and the interior skin of the milling drum where it leads to increased friction and wear and, ultimately, to a loss in performance. In extreme cases, the milled material can become wedged in the gap and block the milling drive which can cause considerable damage to the road milling machine. This is aggravated further by the fact that not only the narrow gap alone but the wedged shape of the gap causes the problems when a milling drum of circular cross-section is put over an extension housing that is eccentric or non-rotationally symmetrical to the output shaft. Owing to the wedged shape and with a stationary extension housing and rotating milling drum, the milled material is drawn into the gap and compressed.
A further disadvantage of the known prior art is that milling drums with a relatively small diameter or a spherical shape cannot be used due to the fact that the gearbox housing makes almost full use of the free interior space of the milling drum towards the top.
Finally, a further disadvantage of the known design is to be seen in the fact that the housing part located outside of the drum casing is at a higher level than the housing part located inside the drum casing, thus necessitating two separate oil supply systems. The separate oil supply systems require additional components, such as pumps or oil coolers, and exhibit temperature problems due to the lack of temperature compensation between the two gearbox parts.